Winter blend gas is a type of gasoline that is sold during the winter months in California. It is different from summer blend gas, which is sold during the summer months. The main difference between the two is the fuels Reid Vapor Pressure (RVP), which is a measure of how easily the fuel evaporates at a given temperature. Winter-blend gas has a higher RVP because the fuel must be able to evaporate at low temperatures for the engine to operate properly. Summer-blend gas has a lower RVP to prevent excessive evaporation when outside temperatures rise. That evaporation can cause vapor lock in an engine on hot days and contributes to unhealthy ground-level ozone and smog levels. According to AAA, winter blend gas is cheaper than summer blend gas because it is able to contain more butane, which is less expensive compared to other gasoline ingredients but also helps your gas ignite in lower temperatures. During the winter gas period, you may notice a price drop from 10 to even 30 cents per gallon, but you also might notice slightly lower gas mileage overall. To mitigate this decrease in gas mileage, AAA recommends keeping tires properly inflated, avoiding rapid acceleration and braking, and using cruise control on the highway when it’s safe to do so.